The proposed project will characterize synaptic pathology in two models of traumatic brain injury. The overall goal of this project is to explore how neural hyperexcitability occurs after blood-brain barrier compromise, as a means to discover how traumatic brain injury leads to posttraumatic epileptogenesis. It is already known that central nervous system exposure to serum albumin via a penetrating head injury can lead to downstream perilesional hyperxcitability and seizures. There is also evidence that this effect is mediated initially by an astrocytic reaction, including activation of a TGF- signaling cascade. However, the exact mechanims by which the astrocytic reaction to serum albumin leads to hyperexcitability is largely unknown. Recent studies have shown that astrocytes can control the strength and number of both excitatory and inhibitory synapses. Furthermore, my preliminary results strongly support an increase in both anatomical and functional excitatory synapses following albumin treatment. Thus, the proposed study will characterize excitatory and inhibitory synaptogenesis in CNS cells exposed to serum albumin. The effects of albumin exposure on synaptic connectivity will be assessed using two model systems. First, primary cultured hippocampal CNS cells, comprising mainly neurons and astrocytes, will be either left untreated or treated with albumin at about one half the concentration found in blood. Second, mice will be implanted with a micro-pump that chronically perfuses albumin at blood concentrations intraventricularly for several days. Synaptogenesis will be assessed in both models after 24 and 72 hours of albumin exposure. These time points were selected because they are prior to the onset of overt epileptic symptoms, thus avoiding potential confounding effects of seizures on synaptic plasticity and reorganization. Anatomical synapses will be counted using immunocyto- or immunohistochemical labeling of synaptic markers, while number and strength of functional synapses will be measured by recording miniature post synaptic currents. The proposed project will contribute significantly to understanding how albumin effects synaptic connectivity. By doing so, the results of this study are expected to greatly enhance our understanding of synaptic pathology underlying posttraumatic epileptogenesis. PUBLIC HEALTH RELEVANCE: The proposed project will explore mechanisms underlying heightened neural excitability in two models of traumatic brain injury. By characterizing synaptic reorganization following central nervous system exposure to serum albumin, the results of this study will contribute significantly to the understanding of how albumin extravasation following head trauma can lead to epileptogenesis. Furthermore, by dissociating different effects of albumin on the development of synaptic reorganization, I expect to identify possible targets for therapeutic prevention of posttraumatic epileptogenesis.